Photovoltaic Backsheet

Abstract

Backsheets and coating compositions for forming such are described which are useful in photovoltaic modules. Various coating compositions are described which provide improved properties for the backsheet.

1 . A photovoltaic backsheet comprising a cured coating disposed on a substrate, the coating prior to curing including polyvinylidene fluoride and at least one acrylic polymer, wherein the weight percent of the at least one acrylic polymer is from about 20% to about 40% based upon the total weight of the polyvinylidene fluoride and the at least one acrylic polymer. 
     
     
         2 . The photovoltaic backsheet of  claim 1  wherein the weight percent of the at least one acrylic polymer is about 20%. 
     
     
         3 . The photovoltaic backsheet of  claim 1  wherein the polyvinylidene fluoride is selected from the group consisting of copolymers of vinylidene fluoride and hexafluoropropylene, homopolymers of polyvinylidene fluoride, and combinations thereof. 
     
     
         4 . The photovoltaic backsheet of  claim 1  wherein the acrylic polymer is formed from methyl methacrylate, n-butyl methacrylate, hydroxyethyl methacrylate, and methacrylic acid. 
     
     
         5 . The photovoltaic backsheet of  claim 1  wherein the coating prior to curing also includes a crosslinker, wherein the weight percent of the crosslinker is from about 7% to about 10% based upon the total weight of the polyvinylidene fluoride and the at least one acrylic polymer. 
     
     
         6 . The photovoltaic backsheet of  claim 5  wherein the crosslinker is a melamine crosslinker. 
     
     
         7 . The photovoltaic backsheet of  claim 1  wherein the coating prior to curing also includes pigment and binder, wherein the weight ratio of the pigment to the binder is from about 0.1 to about 1.1. 
     
     
         8 . The photovoltaic backsheet of  claim 1  wherein the weight ratio of pigment to binder is from about 0.5 to about 0.9. 
     
     
         9 . The photovoltaic backsheet of  claim 1  wherein the weight ratio of pigment to binder is from about 0.6 to about 0.7. 
     
     
         10 . The photovoltaic backsheet of  claim 1  wherein the thickness of the coating prior to curing is from about 0.1 mil to about 1 mil. 
     
     
         11 . The photovoltaic backsheet of  claim 1  wherein the thickness of the coating prior to curing is from about 0.25 mil to about 0.75 mil. 
     
     
         12 . The photovoltaic backsheet of  claim 1  wherein the thickness of the coating prior to curing is from about 0.25 mil to about 0.5 mil. 
     
     
         13 . The photovoltaic backsheet of  claim 1  wherein the thickness of the coating prior to curing is about 0.25 mil. 
     
     
         14 . The photovoltaic backsheet of  claim 1  wherein the UV transmission of the coating after curing is less than 0.12%. 
     
     
         15 . The photovoltaic backsheet of  claim 1  wherein the substrate includes polyester. 
     
     
         16 . The photovoltaic backsheet of  claim 15  wherein the polyester is polyethylene terephthalate. 
     
     
         17 . The photovoltaic backsheet of  claim 1  further comprising a layer of ethylene vinyl acetate. 
     
     
         18 . The photovoltaic backsheet of  claim 17  wherein the layer of ethylene vinyl acetate is adjacent to the coating. 
     
     
         19 . A photovoltaic backsheet comprising a cured coating on a substrate, the coating prior to curing comprising:
 from about 20 to about 40 parts by weight of at least one acrylic polymer;   from about 50 to about 120 parts by weight of polyvinylidene fluoride;   from about 1 to about 20 parts by weight of crosslinker; and   from about 50 to about 120 parts by weight of pigment.   
     
     
         20 . The photovoltaic backsheet of  claim 19  wherein the amount of the acrylic polymer is about 30 parts by weight. 
     
     
         21 . The photovoltaic backsheet of  claim 19  wherein the acrylic polymer is formed from methyl methacrylate, n-butyl methacrylate, hydroxyethyl methacrylate, and methacrylic acid. 
     
     
         22 . The photovoltaic backsheet of  claim 19  wherein the amount of polyvinylidene fluoride is about 70 parts. 
     
     
         23 . The photovoltaic backsheet of  claim 19  wherein the polyvinylidene fluoride is selected from the group consisting of copolymers of vinylidene fluoride and hexafluoropropylene, homopolymers of polyvinylidene fluoride, and combinations thereof. 
     
     
         24 . The photovoltaic backsheet of  claim 19  wherein the polyvinylidene fluoride is a copolymer. 
     
     
         25 . The photovoltaic backsheet of  claim 19  wherein the polyvinylidene fluoride is a homopolymer. 
     
     
         26 . The photovoltaic backsheet of  claim 19  wherein the crosslinker is a melamine crosslinker. 
     
     
         27 . The photovoltaic backsheet of  claim 19  wherein the amount of crosslinker is about 7 parts by weight. 
     
     
         28 . The photovoltaic backsheet of  claim 19  wherein the amount of pigment is about 78 parts by weight. 
     
     
         29 . The photovoltaic backsheet of  claim 19  wherein the pigment is a dispersion of titanium dioxide in a binder. 
     
     
         30 . The photovoltaic backsheet of  claim 29  wherein the dispersion contains about 60% titanium dioxide dispersed in a binder. 
     
     
         31 . The photovoltaic backsheet of  claim 19  wherein the coating prior to curing further comprises from about 70 to about 160 parts by weight solvent. 
     
     
         32 . The photovoltaic backsheet of  claim 31  wherein the amount of the solvent is about 100 parts by weight. 
     
     
         33 . The photovoltaic backsheet of  claim 32  wherein the solvent is selected from the group consisting of cyclohexanone, acetate ester, butyrolactone, and combinations thereof. 
     
     
         34 . The photovoltaic backsheet of  claim 32  wherein the solvent includes cyclohexanone, acetate ester, and butyrolactone. 
     
     
         35 . The photovoltaic backsheet of  claim 19  wherein the coating further comprises a dispersant. 
     
     
         36 . The photovoltaic backsheet of  claim 19  wherein the coating further comprises a catalyst. 
     
     
         37 . The photovoltaic backsheet of  claim 19  wherein the coating further comprises a UV absorber. 
     
     
         38 . The photovoltaic backsheet of  claim 19  wherein the coating further comprises an antioxidant. 
     
     
         39 . The photovoltaic backsheet of  claim 19  wherein the substrate includes polyester. 
     
     
         40 . The photovoltaic backsheet of  claim 39  wherein the polyester is polyethylene terephthalate. 
     
     
         41 . The photovoltaic backsheet of  claim 19  further comprising a layer of ethylene vinyl acetate adjacent to the coating. 
     
     
         42 . The photovoltaic backsheet of  claim 19  wherein the UV transmission of the coating after curing is less than 0.12%. 
     
     
         43 . A photovoltaic backsheet comprising a cured coating disposed on a substrate, the coating prior to curing comprising:
 from about 80 to about 120 parts by weight of at least one fluorinated vinyl ether;   from about 5 to about 35 parts by weight of at least one isocyanate crosslinker; and   from about 50 to about 150 parts by weight of pigment dispersion.   
     
     
         44 . The photovoltaic backsheet of  claim 43  wherein the amount of fluorinated vinyl ether is about 100 parts by weight. 
     
     
         45 . The photovoltaic backsheet of  claim 43  wherein the fluorinated vinyl ether is a fluoroethylene-alkyl vinyl ether. 
     
     
         46 . The photovoltaic backsheet of  claim 43  wherein the amount of isocyanate crosslinker is from about 9 to about 28 parts by weight. 
     
     
         47 . The photovoltaic backsheet of  claim 43  wherein the coating prior to curing further comprises from about 0.5 to about 1 part by weight of UV absorber. 
     
     
         48 . The photovoltaic backsheet of  claim 47  wherein the amount of UV absorber is about 0.72 parts by weight. 
     
     
         49 . The photovoltaic backsheet of  claim 43  wherein the coating prior to curing further comprises from about 1 to about 10 parts solvent. 
     
     
         50 . The photovoltaic backsheet of  claim 49  wherein the amount of solvent is about 5 parts by weight. 
     
     
         51 . The photovoltaic backsheet of  claim 50  wherein the solvent is 2,4-pentane dione. 
     
     
         52 . The photovoltaic backsheet of  claim 43  wherein the amount of pigment dispersion is from about 80 to about 130 parts by weight. 
     
     
         53 . The photovoltaic backsheet of  claim 43  wherein the pigment includes titanium dioxide. 
     
     
         54 . The photovoltaic backsheet of  claim 43  wherein the pigment dispersion includes titanium dioxide and a solvent selected from the group consisting of propylene glycol monomethyl ether acetate (PMAC), xylene, and combinations thereof. 
     
     
         55 . A photovoltaic module comprising:
 at least one solar cell; and   a backsheet disposed on the solar cell, the backsheet comprising a cured coating disposed on a substrate, the coating prior to curing including polyvinylidene fluoride and at least one acrylic polymer, wherein the weight percent of the at least one acrylic polymer is from about 20% to about 40% based upon the total weight of the polyvinylidene fluoride and the at least one acrylic polymer.   
     
     
         56 . The photovoltaic module of  claim 55  wherein the polyvinylidene fluoride is selected from the group consisting of copolymers of vinylidene fluoride and hexafluoropropylene, homopolymers of polyvinylidene fluoride, and combinations thereof. 
     
     
         57 . The photovoltaic module of  claim 55  wherein the acrylic polymer is formed from methyl methacrylate, n-butyl methacrylate, hydroxyethyl methacrylate, and methacrylic acid. 
     
     
         58 . The photovoltaic module of  claim 55  wherein the coating prior to curing also includes a crosslinker, wherein the weight percent of the crosslinker is from about 7% to about 10% based upon the total weight of the polyvinylidene fluoride and the at least one acrylic polymer. 
     
     
         59 . The photovoltaic module of  claim 55  wherein the substrate is polyethylene terephthalate. 
     
     
         60 . The photovoltaic module of  claim 55  wherein the UV transmission of the coating after curing is less than 0.12%. 
     
     
         61 . A photovoltaic module comprising:
 at least one solar cell; and   a backsheet disposed on the solar cell, the backsheet comprising a cured coating on a substrate, the coating prior to curing comprising:   from about 20 to about 40 parts by weight of at least one acrylic polymer;   from about 50 to about 120 parts by weight of polyvinylidene fluoride;   from about 1 to about 20 parts by weight of crosslinker; and   from about 50 to about 120 parts by weight of pigment.   
     
     
         62 . The photovoltaic module of  claim 61  wherein the acrylic polymer is formed from methyl methacrylate, n-butyl methacrylate, hydroxyethyl methacrylate, and methacrylic acid. 
     
     
         63 . The photovoltaic module of  claim 61  wherein the polyvinylidene fluoride is selected from the group consisting of copolymers of vinylidene fluoride and hexafluoropropylene, homopolymers of polyvinylidene fluoride, and combinations thereof. 
     
     
         64 . The photovoltaic module of  claim 61  wherein the substrate is polyethylene terephthalate. 
     
     
         65 . The photovoltaic module of  claim 61  wherein the UV transmission of the coating after curing is less than 0.12%. 
     
     
         66 . A photovoltaic module comprising:
 at least one solar cell; and   a backsheet disposed on the solar cell, the backsheet comprising a cured coating disposed on a substrate, the coating prior to curing comprising:   from about 80 to about 120 parts by weight of at least one fluorinated vinyl ether;   from about 5 to about 35 parts by weight of at least one isocyanate crosslinker; and   from about 50 to about 150 parts by weight of pigment dispersion.   
     
     
         67 . The photovoltaic module of  claim 66  wherein the fluorinated vinyl ether is a fluoroethylene-alkyl vinyl ether. 
     
     
         68 . The photovoltaic module of  claim 66  wherein the pigment includes titanium dioxide. 
     
     
         69 . A method of forming a photovoltaic backsheet, the method comprising:
 providing a substrate in the form of a thin film or sheet;   obtaining a composition including polyvinylidene fluoride and at least one acrylic polymer, wherein the weight percent of the at least one acrylic polymer is from about 20% to about 40% based upon the total weight of the polyvinylidene fluoride and the at least one acrylic polymer;   applying a coating of the composition on the substrate;   curing the coating on the substrate to thereby form the photovoltaic backsheet.   
     
     
         70 . The method of  claim 69  wherein the applying of the coating is performed by at least one technique selected from the group consisting of reverse roll, gravure, slot die, meyer rod, spray, and combinations thereof. 
     
     
         71 . The method of  claim 69  wherein curing is performed by heating the coating to a temperature of from about 138° C. to about 182° C. for a time period of from about 1 minutes to about 5 minutes. 
     
     
         72 . A method of forming a photovoltaic backsheet, the method comprising:
 providing a substrate in the form of a thin film or sheet;   obtaining a composition including from about 20 to about 40 parts by weight of at least one acrylic polymer, from about 50 to about 120 parts by weight of polyvinylidene fluoride, from about 1 to about 20 parts by weight of crosslinker; and from about 50 to about 120 parts by weight of pigment;   applying a coating of the composition on the substrate;   curing the coating on the substrate to thereby form the photovoltaic backsheet.   
     
     
         73 . The method of  claim 72  wherein the applying of the coating is performed by at least one technique selected from the group consisting of reverse roll, gravure, slot die, meyer rod, spray, and combinations thereof. 
     
     
         74 . The method of  claim 72  wherein curing is performed by heating the coating to a temperature of from about 138° C. to about 182° C. for a time period of from about 1 minutes to about 5 minutes. 
     
     
         75 . A method of forming a photovoltaic backsheet, the method comprising:
 providing a substrate in the form of a thin film or sheet;   obtaining a composition including:
 from about 80 to about 120 parts by weight of at least one fluorinated vinyl ether; 
 from about 5 to about 35 parts by weight of at least one isocyanate crosslinker; and 
 from about 50 to about 150 parts by weight of pigment dispersion; 
   applying a coating of the composition on the substrate; curing the coating on the substrate to thereby form the photovoltaic backsheet.   
     
     
         76 . The method of  claim 75  wherein the applying of the coating is performed by at least one technique selected from the group consisting of reverse roll, gravure, slot die, meyer rod, spray, and combinations thereof. 
     
     
         77 . The method of  claim 75  wherein curing is performed by heating the coating to a temperature of from about 93° C. to about 182° C. for a time period of from about 1 minute to about 5 minutes.